Check out the following URLs:
http://www.adobe.com/devnet/captivate/articles/filesize.html
http://rajntechnlife.wordpress.com/2007/02/16/how-to-reduce-captivate-fileswf-size/
http://elearninglive.com/wordpress/2007/04/captivate-file-size-tips/
http://elearningtech.blogspot.com/2006/03/captivate-file-size-tricks-for.html